Combustion control system



Dec. 15, 1931. T BENJAMIN 1,836,786

COMBUSTION CONTROL SYSTEM File'a Dec. 1, I928 2 Sheets-sheet 1 IndicatorINVENTOR MPPIH G.Ben amm TTO'RNEY Dec."15, 1.931. M. G. BENJAMIN1,336,786

I I COMBUSTION CONTROL SYSTEM Filed Dec. 1, 1928 Sheets-Sheet 2 lNVENTORMerrill GBeruamm ATTORN EY Patented Dec. 15, 1931 MERRILL ejnnnanmm, orLAKEWOOD, OHIO ooivmus'rron CONTROL sYs'rEM Application filed December 11928; Serial No. 323,145.

My invention pertains to systems for controlling combustion and, inparticular, to systems of the type mentionedwhich are applicable to thefurnaces of a steam-boiler 5 plant.

The principal object of my invention is the provision of acombustion-control system that shall be entirely automatic in itsoperation.

Another object of my invention is to provide a control system whichshall be responsive to the steam pressure in a boiler or in the outputmain connecting a plurality of boilers, if such is provided, and shalloperate to maintain a constant predetermined pressure therein. s

Anotherobject of my invention is to pro vide a control system in which avariation in steam pressure causes the operation of means,

such as boiler and furnace auxiliaries, to restore the steam pressure toits normal value, the speed of the various auxiliary-controlling meansbeing made proportional to the magnitude of the variation of the steampressure from normal.

Another object of my invention is to provide means for decelerating theadjustment of the boiler and furnace auxiliaries when the steam pressuretends to return to normal.

Another object of my invention is to provide indicating means at acentral point for indicating the adjustment of a plurality of boiler andfurnace auxiliaries.

Another object of my invention is to provide means for supplementallycontrolling the adjustment of the various auxiliaries'in accordance withcertain functions" of the boiler and furnacewhich will be described inmore detail hereinafter.

I am aware that it haspreviously been proposed to control the forceddraft supplied to boiler furnaceby varying the position of an inletdamper or by varying the speed of a forced-draft fan in accordance: withthe 4.5 boilersteam pressure and that the control of the induced'draftby similar means has also been suggested. I understand, also, that ithas previously been the practice to control the rate of fuel feed to afurnace by varying the speed of a motor-driven stoker by the samefunction of the boiler. I propose, however, to make use of thesefundamentalprinciples in a nevwcombination which shall function'toaccomplish the objects above set forth.

In accordance with the system of my inven- 'tion, I provide amotor-driven, forced-draft fan and a motor-driven induced-draft fan,

. as well as a motor-driven stoker or equivalent fuel-feeding means. Byvarying the speed of these auxiliaries properly, it is possible, ofcourse, to control the rate of combustion in a boiler furnace.- As thesystem of my invention will generally be applied .to a battery ofboilers, such as is usually installed in a steam-electric generatingplant,'my invention 95 contemplates the duplication ofthe controlapparatus to be hereinafter described for one boiler for each of theboilers in the batter As a means for controlling the speed of theboilerand furnace auxiliaries, I have disclosed the rheostatic. control of themotors for driving the auxiliaries, although it is obvious that. anyother known method of in the boiler or steam header, to vary the rate ofcombustion in a similar ratio. In ad- .dition to the primary control bymeans of the steam pressure, my system includes additlonal controliingmeans for the various auxiliaries,independent of the steam-pressureregulator and of each other, for independently controllingthe speed ofany auxiliary of any furnace. These supplemental control meanszareresponsive to certain boiler and .furnace 11.

furnace conditions which will be described in detail later.

For a more complete description of the system of my invention, referenceshould be had to the following specification and the accompanyingdrawings, in which Figure 1 illustrates, diagrammatically, one of aplurality of boilers, together with the control equipment for theforced-draft and induced-draft fan motors thereof and the indicatorstherefor, and

Fig. 2 illustrates the control equipment for the stoker motor of theboiler shown in Fig. 1 and the master steam-pressure regulator, as wellas a second boiler which is adapted to have similar control equipmentassociated with it.

Referring now in detail to both figures of the drawings, furnaces 10 and11 are adapt ed to generate steam in boilers 12 and 13 for supplying aturbine (not shown), for example, connected to the steam header 14.

The furnace 10 is provided with a motordriven fuel feeder 15 which maybe a chaingrate stoker or a feeder for pulverized coal, and also with aforced-draftfan 16 and an induced-draft fan 17. The furnace 11 isprovided with similar auxiliaries, namely, a stoker 18, forced-draft fan19 and induceddraft fan 20. Electric motors 21, 22 and 23 are providedfor driving the forced-draft and induced-draft fans and the stoker ofthe furnace 10 and similar motors 24, 25 and 26 are arranged to drivesimilar auxiliaries of the The motors may be coupled' to the auxiliariesby any known driving means,

but I have illustrated the auxiliaries directly connected to theshaftsof the motors.

From this point on, the description of my invention will refer only tothe auxiliaries of the furnace 10, it being assumed that duplicatecontrol equipment will be provided for the auxiliaries of the furnace11.

The speeds of the auxiliary motors 21, 22

and 23 which drive the forced-draft and inprovide for the adjustment ofthe speeds of the auxiliary motors in accordance with the steam pressureand also in accordance with the variatlon 1n certaln boiler and furnaceconditions; The exact mechanism by which this variation is accomplishedwill now be described in detail.

, 'Connected to the steam header 14 is a Bourdon tube 30 (Fig. 2) orother equivalent means responsive to the steam pressure in the header.Themaster steam-pressure regulator, indicated generallyat 31,'is adaptedto lie-controlled by 'the Bourdon-tube.

This regulator comprises a shaft 32 on which is loosely journalled apivoted contact arm 33, the end of which is connected to the end of theBourdon tube by means of a linl: 34.

A contact-bearing disc 35 is also mounted on the shaft 32 and isprovided with teeth on its periphery for engagement with a worm 36. Acontact arm 37 is mounted on the shaft 32 and is adapted to befrictionally engaged by the disc 35 and rotated therewith until itengages either one of the fixed contacts 38, 39.

The worm-wheel disc 35 is provided with two conducting segments 40 and41, separated by an insulating spacer, which are adapted tobe engaged bythe contact arm 33 when the latter is moved in either direction from thecentral or neutral position in which it is illustrated.

The contact arm 33, under the influence of the Bourdon tube 30, isadapted to con .trol the operation of a motor 42 having forward andreverse field windings 43 and 44. The motor 42 will be referred tohereinafter as the indieator-generator motor because it is directlyconnected to the rotor of a synchronous, polyphase, alternating-currentmachine 45 which'serves to supply current to other electrical. devices,as will be explained more fully in the course of the followingdescription. It 'may be noted, however, at

this point, that the stator of the machine 45 ls'adapted to be energizedfrom any convenient polyphase source. The rotor is connected to set ofmain conductors such as 46 which constitutes an indicator bus.

Connected to the shaft of the motor 42 is a These resistors have currentsources of opposite polarity and thus constitute a so-calledpotentiometer bridge. It will be obvious that, when the arms 48 and 49take up the neutral position in which they are illustrated the. voltagedifference therebetween will be zero and that, as the arms movesimultaneously in the one or the other direction from the neutralposition, a constantly increasing voltage of the one or the otherpolarity will exist thereacross.

The voltage across the arms 48 and 49 is applied to the armature of amotor 52 having a shunt field winding 53. The motor 52 is mechanicallyconnected to the rotor of alternating-current machine 54, similar in allrespects to that shown at 45, which will be referred to as the controlgenerator, since it supplies current to the conductor 56 whichconstitutes a control bus.

It may be desirable to employ a speedredu'ction gear between the motors42 and 52 and the generators 45 and 54, since the latter are designedonly for a relatively limited rotative movement.

Referring again to the contact arm 37, this I may employ a separatereversible motor member is adapted to complete a' circuit for eratic-11of the control apparatus for'the stoker motor 23. V

The shaft of the motor 23, in addition to being connected to the stoker15, has an extension to the operating arm of the speedcontrollingrheostat 29. The connectionbetween the motor shaft and the rheostat arm,however, is not permanent but is adapted to be effected, when desired,by means of a magnetic clutch, indicated at 60, which is of standarddesign and is adapted to be controlled by solenoids 61 and 62. When oneof said solenoids is energized, the clutch so connects the rheostat armto the shaft of the motor 23 that it is rotated in one direction.Energization of the other solenoid of the clutch will cause rotation ofthe rheostat arm in the reverse direction. It will be obvious,therefore, that the setting of the rheostat 29 and, consequently, thespeed of the motor 23, may be varied at will by the successiveenergization of the solenoids 61 and 62 of the clutch 60.. Instead ofthe magnetic clutch for operating the rheostat 29.

For controlling the solenoids of the clutch 60, I provide acontact-making mechanism indicated generally at 63. This mechanismincludes a disc 64 provided with two conducting segments 65 and 66,insulated from each other, which are adapted to be engaged by a contactarm 67 which is actuated in accordance with the movement of shaft 29 onwhich the contact arm of rheostat 29 is mounted. The disc 64 ismechanically coupled to the rotor of a polyphase, synchronous,alternating-current, machine 68 similar to those shown at 45 and 54,except that the machine 68 operates as a motor when supplied withcurrent of suitable characteristics from the control generator 54.

The generator 54 and the motor 68, being supplied with alternatingcurrent from the same source,'tend to maintain theirrotors stationary incorresponding positions. This synchronizing action is well known and hasbeen employed heretofore where it was de sired to move one element insynchronism with another. The theory underlying this operation is knownand, therefore, needs no explanation here. It is sufficient to explainthat any movement of the'rotor of the generator 54 will immediately becommunicated to the rotor of the motor 68 and, therefore, to the contactdisc 64. The positions of the balanced relay disc. 64 and the contactarm 67 .ontheir :respective driving shafts may be reversedif desired. ai :The motor 68, however, differs from the generator 54 in that thestator winding of the motor 68 is adapted to be rotated by means of aworm 69, the motor housing being supported for rotation and provided atits periphery with teeth for engagement by said worm. i I

It will be obvious, of course, that the position ofthe rotor ofthe'motor 68 is controlled not only by the position of the rotor of thegenerator 54 but also by the position of the stator of the motor 68.Thatis to say, the rotor of. the motor 68; may be shifted as aresult ofa shift in the position of the rotor of the generator 54 or of a shiftin the position of the stator .68.

The worm 69 is adapted to be rotated by the movement of the shaft 29which'carries the "contact arm ofthe 'rheostat 29. Connection notpermanent but is effected only when the solenoid 70 of a magnetic clutch71 is ener gized. A manual switch 72 is provided. for controlling theenergization of the solenoid 70 in series with either of the solenoids61 and 62 of the clutch 60 and, in addition, a 73 is also effective tocontrol said solenoids. 7

The relay 73' comprises a pivoted beam adapted to be actuated by aplurality of magnet coils 74, 75 and 76. The coil 74 is connected incircuit with'a rehostat 77, the contact arm offwhich isdriven by theshaft 29. -The ,energization of the coil 74, therefore,

varies directly with the "speed of the stoker motor 23 which, as pointedout previously,

responds directly tovariations inthe steam' pressure in the header 14.The. coil 75 is energized under the control of a steam-flow meter'7 8which is so connected as to measure the steam output .of' the boiler 12.The coil 7 6, similarly, isenergized under the control of a feed-waterinput flow meter 79 which measures the flow of feed water into theboiler 12. It'will be-understood that the feed water is supplied to theboiler from the usual feed-water heater by means of a pump, not shown,-through the pipe 80.

The steanrflowmeter 78 andthe feed-water flow meter 79 areistandarddevices and are,

- therefore, not described in detail.

The motor 83 moves in synchronism with i ly, moves in synchronism withthe generator ence in voltage across the arms 48 and 49, conshaft 29'.

54. The two pointers on the dial 82, therefore, acquaint the stationoperators with the actual steam pressure in the header and theadjustment of the speeds of the various auxiliaries to restore thepressure to normal.

The indicator 85 is driven by the indicator motor 86 which isconnectedto the rotor of an indicator generator 87 mounted on the The indicator85, therefore, always shows the position of the rheostat 29 whichcontrols the speed of the stoker motor 23.

Having described the master control regulator and the controlapparatus'for the stoker motor in detail, I shall now explain the methodof operation of my system. In this description, it will be assumed firstthat the steam pressure in the header 14 is at its normal value, thatthe steam-pressure regulator 31 and all of its elements are in theirneutral positions, that the motors 42 and 52 are stationary and that thestoker motor 23 is rotating atnormal speed, at which suflicient fuel issupplied to the grate to maintain normal boiler pressurefor normaldemand on the station. It will also be assumed that the contact memberof the relay 73 is in the neutral position, as well as the switch 72 andthe contact 67.

mal value, as a result of an increase in the station load, for example,the Bourdon tube will contract and, through the link 34, will cause thecontact arm 33 of the pressure regusults in the completion of a circuitthrough theforward field winding 43 and armature of the motor 42 whichthereupon begins to rotate. As the motor 42 rotates, it shifts theposition of the rotor of the indicator generator 45, shifts the arms 48and 49' of resistors 50 and 51 away from the neutral position and, atthe same time, tends to restore the disc to a position in which the arm33 engages the insulating spacer between the conducting segments and 41.When this restoration has been accomplished, further rotation of themotor 42 is-stopped. The shifting of the rotor of the generator causes acorresponding shift in the position of the pointer actuated by the motor83 on the control panel. Y

The motor 52, being subject to the differtinues to turn the rotor of thecontrol generator 54. The rotor of the generator 54 causes acorresponding shift in the position of the rotor of the motor 68 whichthereupon moves the disc 64 so that the contact arm 67 engages one ofthe conducting segments 65, 66. A

circuit is thereby completed for one of the solenoids 61, 62 of themagnetic clutch to cause a'mov'ement of the shaft 29 in such directionthat the rheost-at 29 will be adjusted to increase the speed of thestoker motor 23 so that the rate of combustion in the furnace 10 willlikewise be increased and the boiler pressure restored to normal.

As the adustment of the rheostat 29 proceeds, the contact arm 67 isreturned to its neutral position between the segments 65 and 66 andfurther ad ustment of the stoker motor rheostat is stopped. The movementof the rheostat arm 29 is indicated on the board 81 by means of theindicator motor 86 and the indicator 85.

The control-generator motor 52 continues to shift the position of therotor of the conwill engage the fixed contact 39 to energize the relay57 which short-circuits the resistor 58 in the circuit of the shuntfield winding 53 of'the motor 52 to further decrease the speed of thelatter. If the restoration. of the steam pressure proceeds at acomparatively slow rate, however, the speed of the motor 52 is decreasedonly by the return of the rheostat arms 48, 49 to the neutral position.In any ease, the speed of the motor 52 is dependent upon the differencebetween the actual header pressure and normal pressure.

lator 31 to engage the segment 41. This refunction. It operates tocontrol the speed of I the stoker motor supplementally so that the motorspeed will be further adjusted in accordance with conditions in theboiler 12.

If the quality of the fuel supplied to the stoker 15 varies, forexample, the actual amount of combustible fuel supplied to the gratewill likewise vary. If coal of a lower grade is placed in the stokerhopper, less heat will be supplied by the furnace to the boilera-nd'less steam generated thereby. The steam output of the boiler willthereby be decreased and this decrease will be registered by a change inthe energization of the coil which is controlled by the steam-flow meter78. This change. in the energization of the coil 75 of the relay 73 willcause the pivoted beam of said relay to move so that its contact armwill engage one of the fixed contacts to energize the coil 7 O ofthe-clutch 71 in series with one of the coils 61, 62 or of the clutchice llt The energization of the coils 61, 62 will cause an adjustment ofthe Stoker-motor rheostat 29, as explained-heretofore. The simultaneousenergization of the coil 70 will cause a shift in the position of thestator of the motor 68 which has the effect of further. adjusting theposition of the stoker-motor rheostat through the contact mechanism 64to 67. It will thus be apparent that a change in the grade of-the fuelsupplied to the furnace will cause a change in the Stoker-motor speed sothat more or less coal will be supplied per 'unit of time to compensatefor the decrease in the percentage of combustible matter in the coal andto maintain a constant'supply of combustible matter per unit of time forany given setting of the master regulator.

A similar resultis effected by a changein the rate of feed-water supply.Ordinarily,

feed water is supplied at a definite rate and at a definite temperature.If anything happens to vary the rate of feedwater supply, for example,the failure of the feed-water pumps (not'shown), the energization of thecoil 7 6 of the relay 73 will be so changed by the operation of thefeed-water flow meter 79 as to adjust the setting of the stoker-motorrheostat 29, in the manner described above, to decrease the amount ofcoal supplied to the furnace.

It will be apparent that the supplemental control of the stoker motor 7automatically regulates the supply of fuel to the furnace in accordancewith the amount of heat absorbed by the boiler. The heat absorption ofthe boiler is measured by the difference between the heat'in the steamoutput andthat in the feed-water input- The relay 73 may readily becalibrated to effect any desired control in accordance with thecharacteristics of the boiler operation. The amount offuel supplied tothe furnace, in other words, is variedin accordance with the amount ofheat absorbed by the boiler.

The manual switch 72 may be employed to eifect the control of thestoker-motor rheostat in the same manner as that described heretofore inconnection with the relay 73, the contacts of the switch 7 2 being inparallel with those of the relay 73. The switch 72 may preferably bemounted onthe control panel 81'instead of in the position shown.

The control of the forced-draft and induced-draft fanmotors 21 and 22 iseffected in a manner similar to that described above for the stokermotor 23, the only difference being in the functions of the boiler andfurnace to which the supplemental control'for these auxiliaries isresponsive.

21 is adjusted in response to themovements of the master steam-pressureregulator 31 in identically the same manner as the speed of the stokermotor. The supplemental control of the speed of the forced-draft motoris,

The speed of the forced-draft fan motor however, effected by abalancedrelay 87 which comprises a'pivoted beam and solenoids'88 and89 foractuating a contact arm mounted on the beam into engagement with one oftwo fixed-contacts 90. The solenoid 88 is energizedin accordance withthe power input to the forced-draftfan motor 21, being connected to ashunt'91 in the motor circuit or other equivalent power-measuringdevice.

Since the voltage of the motor circuit is sub stantially constant, thecurrent input is a measure of the power input. The solenoid 89 isenergized in accordance with the operation of an air-pressure regulator92 which is similar tothe steam-flow-meter 78 in that it produces anelectric current proportional tothe air pressure in the duct'between thefan 16'and the ashpit of the furnace 10.

The supplemental control of the forceddraft. fan motor, therefore, maybe said to be responsive to the difference between the power input tothe fan motor and the forceddraft'air pressure.

By employing these functions, it is possible, by proper calibration ofthe relay 87, tomaintain a constant rateof air supply to the furnace,that is to say, the weight of air supplied per minute is maintainedconstant, at the rate fixed by the position of the master regulator, forall conditions of boiler load. I

The supplemental control of the induced by the the same means describedin connec-- tion withthe stoker motor, when the furnace pressure tendsto lncrease. The furnace pressure, therefore, is maintained atsubstantially a constant value, since an increase therein tends toincrease the speed of the induced-draft fan which tends to decrease thefurnace pressure. v a

It will be understood, of course, that, if the header pressure increasesabove normal,

a corresponding adjustment of all the boiler and-furnace auxiliarieswill be effected to decrease the rate of combustion.

The positions of the rheostats 27 and 28 which control the speedsof theforced-draft and induced-draft fan motors 21 and 22 may be indicatedonthe control panel 81 bythe indicators 94 and 95 which are driven bythe indicator motors 96 and 97. Thesemotors.

are actuated, respectively, by the indicator generators 98 and 99 whichare mechanicall zoupledgto the arms of the rheostats 27 and 28 Aspreviously stated, the control equipment 7 illustrated and described forthe auxiliaries of the furnace 10 are to be duplicated for theauxiliaries of the furnace 11. It is to understood that all auxiliariesof all boilers are simultaneously controlled by the master pressureregulator 81 and that the speed of anyauxiliary of any boiler may beindepend- 1 ently. controlled by its individual supplemen- -.tal controlequipment. This arrangement obviates the inflexibility of the systems ofthe prior art in which all auxiliaries are actuated in response to steampressure and, at the same time, retains the advantage of a--;simultaneous primary control of all auxiliaries, still permittingindividual adjustment of any auxiliary.

Although I have shown and described only a single embodimentof thesystem of my in- "jVel'ltlOIl, it is not my intention to be limitedthereto since my invention is susceptible of various changes andmodifications.

It is to be particularly understood that the application of the systemis not limited to installations of two boilers but may be extended tocontrol automatically almost any number of boilers and furnaces. Asalready stated, the scope of my invention is not to be limited by anyof'the details of the showing fand description but only by the terms ofthe appended claims.

I claim as my invention: I 1. In a furnace-control system, a boiler, afurnace, motor-driven auxiliaries for supplying air and fuel to saidfurnace and ex hausting gases therefrom, a regulator 'responsive to thesteam pressure in said boiler, a controller actuated by saidregulator,'motors controlled by said controller, alternating-currentmachines having rotors driven by said motors, and additionalalternatingcurrent machines having rotors electrically connected to andmoving in synchronism with the rotors of said first-mentioned machinesfor actuating indicators and control devices for varying the speeds ofthe motors driving said auxiliaries.

2. In a furnace-control system, a boiler, a furnace, motor driven fueland air-supplying means and exhaust means for said furnace, a pressureregulator responsive to the pressure of steam in said boiler,speed-controlling means for the motors driving said auxiliaries andmeans for transmitting the movement of said regulator to saidspeed-controlling means comprising a motor controlled by said regulator,an alternating-current generator driven by said motor andalternating-current motors connected to the generator so as to besynchronously driven by said generator for actuating saidspeed-controlli means.

3. In a furnace-control systen a boiler, a furnace and means forsupplying fuel and air to the furnace and exhausting gases thereoo'from,a control mechanism including alternating-current machines, motors fordriving said machines and means for varying the speed of one of themotors in accordance with the departure of boiler steam pressure from sonormal, additional alternating-current machines connected to and movingin synchronism with said first-mentioned'machines for controlling thespeed of thefuel and air-supplying means and the gas-exhausting means,and means for supplementally controlling the speed of the fuel andair-supplying and gas-exhausting means.

1-. In a furnace-control system, a boiler, a furnace, operativeauxiliaries therefor including a stoker, forced and induced-draft fansfor said furnace, means responsive to a condition of said boiler forcontrolling the speed of said auxiliaries and means respon-.

sive respectively to the difference between the heat output from andtheheat output to the boiler, the forced-draft pressure, and the furnacepressure, for supplementally controlling the speed of said auxiliaries.

5. Ina furnace-control system, a boiler, a furnace, means for varyingthe rate of COHl-a bustion in said furnace in inverse proportion to theboiler steam pressure, and means for varying the rate of operation ofsaid combustion-varying means in accordance with the magnitude of thedeparture of boiler steam pressure from normal.

6. In a steam-generating system, a boiler, a furnace, auxiliaries forcontrolling the rate of combustion in said furnace including aforced-draft fan, a motor for driving said fan, and means jointlyresponsive to the forced-draft pressure and to the power input tosaid'motor for controlling the speed of the motor.

7. In a steam-generating system, a boiler, a furnace, auxiliaries forcontrolling the rate of combustion in said furnace including a stoker, amotor for driving said stoker and means jointly responsive to the steampressure in the boiler and to the difference between the steam outputtherefrom and the feed water input thereto for controlling the speed ofthe stoker motor.

8. In a furnace-control system, a boiler, a furnace, and meansresponsive to the boiler steam pressure for controlling the rate ofcombustion in said furnace, and means responsive to the rate of changeof boiler pressure for modifying the operation of saidcombustion-controlling means.

.9. In a furnace-control system, a boiler, a furnace, andcombustion-regulating means for said furnace responsive to the, steampressure in said boiler, a motor for driving said regulating means andmeans responsive to the rate of pressure variation in said, boiler forvarying the speed of said motor;

10. A control system for a boiler furnace including afuel-supplyingmeans therefor, a steam-pressure regulator for controllingsaid means and means responsive to the difference between the amount ofheat delivered by the boiler and the amount of heat supplied thereto inthe feedwater for supplementally controlling said fuel-supplying means.

11. A boiler-furnace combustion-control system comprising a boiler, afurnace, means for controlling the rate of combustion in said furnace,means for controlling the speed of said combustion-rate-controllingmeans in proportion to the magnitude of the departure of the boilersteam pressure from its normal value, and means for further controllingthe speed of said rate-controlling means in accordance With the rate ofrestoration of the boiler steam pressure to normal.

12. In a furnace-control system for a boiler, auxiliaries forcontrolling the rate of combustion in said furnace and 'means forcontrolling said auxiliaries including an alternating current generator,a steam-pressure-responsive means for controlling the rotation of saidgenerator and a plurality of alternating current motors connected to andoperating synchronously With said generator for actuating thecontrolling means for said auxiliaries.

13. In a furnace-control system, a boiler,

a furnace, auxiliaries for controlling the rate of combustion in saidfurnace and means for controlling said auxiliaries including a mastercontroller responsive to boiler steam pressure and an auxiliarycontroller, synchronously operating alternating current machinesconnected to said controllers whereby the auxiliary controller isactuated by and moves in synchronism With said master controller.

14. A system for controlling the rate of combustion of fuel in a boilerfurnace, to build up and maintain a predetermined steam pressure in saidboiler comprising auxiliaries for supplying fuel and air to saidfurnace, a master regulator responsive to the boiler steam pressure foradjusting the speeds of said auxiliaries and a single supplementalcontrol device responsive to a plurality of boiler and furnaceconditions for further adjusting said speeds.

15. In a combustion-control system, the combination With a boiler, afurnace, fuel and air-supplying means for the furnace, of means forcontrolling the fuel and air-supplying means including a primaryregulator actuated by the pressure of the steam in the boiler and asupplemental regulator responsive to the energy-consumption of saidair-supplying means.

16. A control system for a boiler furnace, comprising fuel andair-supplying means for said furnace, a master steam-pressure regulatorfor controlling said means and supplemental regulators for said means,and means for causing the action of said supplemental regulators to varyin proportion to the departure of boiler steam pressure from its normalvalue.

17 A control system for a boiler furnace comprising means for supplyingan element of combustion to said furnace, a master steam-pressureregulator for controlling said means and a single supplemental controlmeans responsive to a plurality of conditions in said boilerand furnacefor further controlling said first-mentioned means.

In testimony whereof, I have hereunto subscribed my name this 19th dayof November, 1928.

MERRILL G. BENJAMIN.

